[Collins] KWM-2 PTT Relay

[Gerald]

On Mon, 2005-11-28 at 09:17 -0500, Gary Franklin wrote:
> I know this has been asked 100 times so I know many of you have a good 
> answer for this!  My KWM-2 PTT relay hangs up when I release the mic ptt. 
> What is the likely culprit?
> 
> Thanks in advance!
> 
> Gary K8BKB 

There are a couple possibilities. One is too much VOX gain. If you are
using PTT, VOX gain should be zero. The other is that there are a pair
of resistors in parallel supplying bias to the cathode of the VOX relay
tube. They were poorly chosen and tend to overheat and to drift in
value. R20 and R47, each 68K. As they drift high they lower the
threshold on the relay tube. Good resistors would be a pair of 68K 2 or
3 watt flame proof metal film resistors such as Mouser 594-5093NW68K00J
or 283-68K. They don't drift with heat or time nearly as much as the
original carbon comp resistors.

And it could be a gassy VOX tube.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer